1. Field of the Invention
The present invention relates to resin panels and more particularly to resin panels requiring structural reinforcement to increase resistance to deformation.
2. Technology Review
It is known to make outer panels of a vehicle body from a resin material by injection molding techniques. Such outer resin panels often require structural reinforcement to increase resistance to deformation by a force applied to an exterior surface of the panel. For example, an outer resin panel of a vehicle door assembly requires reinforcement in the upper region of the panel where the panel is curved toward the top edge bordering the windowsill. Such reinforcement is required in order to meet squeeze test specifications to which the door panels are subjected.
In the past, such structural reinforcement to increase the strength and stiffness of the top region of the door outer resin panel was provided by bonding a separate piece to the inner surface of the outer panel between the front and rear edges thereof to form a hollow truss section. This is shown in FIG. 1 which illustrates a cross-section of the upper region of such a door panel wherein a separate piece 2 is bonded to the inner surface of an outer door panel 4 for creating a truss section 6. As can be seen, this creates a double thickness in the region of the bonds 8. This has the undesirable result that sink marks occur at the outer surface of the outer panel that correspond to the bonded surface. The sink marks damage the quality of appearance of the exterior surface of the outer panel. Moreover, the bonding of a separate reinforcement part to the outer panel results in higher manufacturing costs due to the additional expenses required for the tooling required to make the separate part and for bonding the two parts together. Furthermore, the overall weight of the outer panel is increased due to the double wall thickness in the region of the bond.
Another construction that has been considered to solve the requirement for structural reinforcement in the area of the curved upper region of an outer door resin panel is shown in FIG. 2 wherein ribs 10 and 12 are molded as integral parts to the inner surface of outer door panel 4. While such ribs increase the stiffness of the panel in its upper curved region, such integrally molded ribs also create sink marks in the exterior surface opposite the location of the ribs, damaging the quality of appearance of the exterior surface of the panel.